Receiver for high-frequency electric signals



Jab. 27, 1931. v w. J. BROWN ET AL 1,

RECEIVER FOR HIGH FREQUENCY ELEdTRIC SIGNALS i Filed March 31, I926 2 Sheets-Sheet l 47mm I Jan. .27, 1931. -w. J. BROWN ET AL RECEIVER FOR HIGH FREQUENCY ELECTRIC SIGNALS 2 Sheets-Sheet 2 Filed March 31, 1926 INVENTORS Wa/ferx/ohn Bro warn and WITNESSES:

ATTORNEY Patented Jan. 27 1931 W S i WALTERJO NBROW or srocxronrgnnn cabin REGINALD euncn ornsran rronn, MANGHESTER,,ENGLA1\TD, ASSIGNOES r0. AssooIATEn-nLnorR cAn INDUSTRIES,

LIMITED, A COMPANY, OE-GREAT BRITAIN 1 ancnivungroa I Ii-FREQUENCY ELE T Ic SIGNALS Application filed March 31, 19 2s, Serial Na; 98,757, and; in G-reat Britain March 31, 1925. v i

This invention relates to receiving apparatus for high frequency electrlc signalsof the type in which a thermionic valve with asso ciatedcircuits is arranged to be set into selfmaintained oscillatio'ntby an incoming signal and inwhich means are provided periodically to stop or quench such self-maintained oscillations.

Receivers 1 of ithis type may be I divided into 7 two kinds, both of which kindsfall'within the scope of the present-"invention l Inthefirst kindrof receiver, theapparatu is tripped byan incoming signal from a stable be hereinafterreferredto as super-regeneray non-oscillatory condition to a stable oscill-a tory condition, so that't-he strength of the selfmaintained oscillations is independent of: the: Strengthof the incoming signal but dependentuponzthe characteristics ofthe valve and the. constants of the associated circuits. "Receivers'ofthis'kind will hereinafter-be referred-teas periodic trigger receivers" 'lnfre'ceivers oft-he second kind the therinionicvalve and its associated circuits arecaused to assume successively and alternately two st'atesj one state is highly unstable, and during this unstable state freei'oscillations are; initiated by an incoming signal their initial amplitude being. proportional to the signal strength and their: rate of increase be};

ing* determined by a the characteristics of the valves and" the constants of the associated circuit-s. llhe other state "is completely stable and in-thi's state oscillations initiated in the first'state die'out" to substantiallyrzero amplitude. Receivers of this second-kind will tive receivers; v

According to the invention ma receiver of 7 4b the type-set forth the thermionic valve which is associated with circuits-so arrangedas to beset intoself-maintained oscillation, has its anode circuit supplied with energy from' a-source of alternating electromotive' force} figuresofthe-drawings;

only. 7

tive receiver it isdesirable that the frequency ofi thesalternabingaelebtromotiveiforce should;

lee-high, .preferablyabove or nearthe limit of audible frequencies, andin any; case higher, 7

than any frequency with which the high fre-' quency signal which is to be received, is-niodulated. For aperiodic triggerreceivert-he frequency of the electromotive force may be much lower,- for example fifty cycles 'per second;

An important feature Ofitll invention consists in means to'apply to the grid. of the valve an alternating bias substantially proportional to and in phase opposed-to the al.-

ternating electromotive forcejapplied to the necessary to apply to the grid-of the valve also-a definitesteady positive bias.

- In order that the invention may readily beunderstood four-embodiments thereof will now be described by wayof examplewith reference'to the accompanying drawings inwhich Fig; 1 represents diagrammatically a simple form of: periodic trigger receiver of which-theano'de circuit is supplied directly from an alternator; Fig.2 shows diagrammatically a periodic trigger receiver-wherein means is provided to-apply an alternating bias to the gridyof: the'valve; Fig. 3' represents diagrammatically; aisuper regenerative receiver wherein-theianode circuit is supplied rom a source-of alternating electromotive force which comprises a three electrode valve;

andFig; l-represents a modification of super,- regeneratl-vereceiver n wh ch means, 1s provided torapply an alternating :bias to thegrid of the valve. (l j 7.

Like-reference numerals indicate like-parts wherever" applicable in each: ofthe several In each 'f' he several figures-ofthe draw- :ings batteries 1 and circuits for heating-the cathode or cathodes of thevalve or valves are omittedifor thesake of clearness and'si'mplic ity. r

l sten ng lie i i isfi thermionic valve is connected to the upper end of a closed oscillatory circuit formed by the nected through a relay 21 shunted by a bypass condenser 22 and through a reaction coil 23 to the anode of the valve. i i i In operation the coupling between the reaction coil 23 andthe grid circuit'inductanc-e and the value of steady potential appliedto the grid. 11 are adjusted so that the arrangement has two stable states, namely, the first state in which the system does not maintain oscillations and a second state inwhich the system when once tripped into oscillation maintains oscillations of amplitude. 1 determined solely by the characteristics of the valve and constants of the circuits.

. It will be appreciated that such oscillations can only be maintained during that half cycle ofthe generator during which the anode 12 is positively electrified with respect to the cathode 13. Signals may be introduced into the grid circuit by coupling the inductance 15 to an aerial or by constructing part of the inductance15 as a frame or loop aerial or by any other known method. Upon receipt of a signal the system is tripped into oscillation during that half cycle of the generator 20 which electrifies the anode '12 positively with respect to the cathode 13. The

oscillations are quenched during that half cycle wherein the anode '12 is negatively electrified with respect to'the cathode 13. If the signal still persists the valve or the system is again tripped into oscillation when the anode reaches -a certain definite positive potentialwith respect to the cathode 13.

The valve in the above described adjustment is working about a point upon the lower bend otits anodecurrent grid-voltage characteristic and consequently when thesystem is-in a state ofos'cillation the mean anode current'of the valve will exceed by 'a con slderable amount the mean anode current wh ch flows when the system'ls not in a state of oscillation. The relay 21 is, therefore, so

adjusted that it is not operated by the normal anode current of the valve but is operated by the mean anode current of the valve when the system is in a state of self-maintained oscillation.

The arrangement shown in Fig. 2 is broadl similar to that illustrated in'Fig; In

thisarrangem'ent howeven'means are provided to ensure that the potential of the grid 11 shall have adefiniterelation'tothat of the anode 12. The generator 20 is connected through a transformer25to the ends of a potential divider 26. One end of the. potential divider 26 isconnected to that end of the potential divider 18 which is connected to the negative pole of the battery 19. The

7 other end of the potential divider 26 is con nected'to the relay 21. The cathode 13 instead ofbeing connected directly to the generator as'illustrated in Fig. 1 is connected to a sliding contact uponthe potential divider 26. The position of this sliding contact adjusted so that the alternating voltage applied. to the grid is substantially equal to that applied to the anode divided by the voltage factor of. the valve. In thesecircu'mstances if the battery 19andpotential divider 18 were omitted the lumped voltage over the'valve would be zero throughout the cycle of the generator 20; consequently it is necessary to provide, by means of the battery 19 and potential divider 18, a suflicient positive bias to the grid 11 to bring the system to the operative condition described in connectionwith Fig. 1.

- It has been. found that the voltage of the alternating supply means which may be used from time to time to such ian'extent as to vary very considerably thesensitivity of the re ceiver shown in Fig. 1., If the tripping of in place of the generator 20 may fluctuate the valve .is so adjusted that it does not os-,

cillate when'no'rmal voltage is applied to the anode-butjso that a very small signal applied to the grid will trip it into oscillation, then it is found that a slight increase in the voltageof the mains or generator 20rwill cause the valve to trip'even in the absence of a signal.

Consequently, reliable working can only .be achieved by adjusting the receiver illustrated in 1 so that a comparatively'strong signal is required to'trip the valve. .It has been' found that by adopting the arrangement illustratedin Fig. .2 the sensitivity of the receiver can be made substantially independent of the voltage amplitude applied to the anode over a wide range of amplitudes:

Referring now to Fig. 3 which illustrates. a simple form of superf-regeneratlve receiver the grid 11*of a valve is connected through a closed oscillatory circuit'consisting'of the inductance 15 and variable condenser 16 and through a by-passcondens er17 to the cathode 13. The by-pass condenser 17 is shunted by .a battery 19 of which the number of cells is adjustable so as to bias the grid 11' appropriately. The anode- 12 is connected, through a reaction coil 23,'through telephones 30, shunted by'by-pass condenser 22, to one end of a closed oscillatory circuit formed by the inductance'311and condenser 32, the other end ofw'hich is'co'nnected to a common lead joining the cathode 13 and the cathode 33 of a second valve. The upper end of-the closed. oscillatory circuit- 31', 32 is also connected,

through a high tension battery or other source of direct electromotive force 34 shunted by a condenser 35, to the anode 36'of the second valve. The grid 37 of the second valve is connected, through a grid condenser 38, shunted by a high resistance 39, and through a reaction coil 40, to the conductor joining the cathodes 13 and 33. The reaction coil 40 is coupled to the inductance 31 so that oscillations are maintained in, the circuit 31, 32. It will thus be seen that an alternating electromotive force only is applied to the anode circuit of the first valve. The frequency of the alternating electromotive force may be adjusted by varying the value of the inductance 31 or condenser 32 or by varying both of these values. The frequency should be higher than the frequency of modulation of any high frequency signal which it is desired to receive and preferably should be near to or above the limit of audibility.

. In operation, the coupling between the inductance 23 and the inductance 15 and the value of steady potential appliedto the grid 11 by the battery 19 is so adjusted that when oscillations are initiated by a signal in the initial value. and will be finally quenched by V closed oscillatory circuit 15, 16 their amplitude is proportional to the amplitude of the signaland so that the rate of increase of amplitude of the oscillations is constant. hen oscillations are initiated inthe circuit 15, 16 during that time the anode 12 is positively electrified in respect to the cathode 13,-such oscillations will build up in amplitude to a value which is proportional to their the positive potential of the anode 12 in respect to the cathodel13 falling to a definite amount. If the frequency of oscillations maintained in the circuit 31, 32 is sufficiently high, telephonically modulated signals may be properly reproduced in the telephones 30.

Fig. 4: illustrates a modification of the kind of super-regeneration receiver shown in Fig. 3 in which means is provided to cause the potential of the grid 11 to bear a definite relationship to the potential of the anode 12.

The junction of the closed oscillatory circuit 15, 16 and the by-pass condenser 17 is connected to an adjustable contact upon a potential divider 18 which is connected across a battery 19. The negative end of the battery 19 is adjustably connected to a point of the inductance 31. The lower end of the inductance 31 is connected to the grid 37 of the second valve and an intermediate point of inductance 31 is connected to the conductor ioining the cathodes 13and 33. The upper end of the inductance 31 is connected to the telephones 30 and through a blocking condenser 42 to the anode 36 of the secondjva'ive.

' The anode 36 of the second valve is connected through a. choke coil 41 to the positivepole from the battery 19 to the inductance "313i s sci-adjusted that the alternating yoltage: ap- 2m plied tothexgrid lliis equal toand opposite in phase to that applied t-OFtl'lB ELHOdG ;12 divided by the voltage factor 1 of the valve. Inthesecircumstancesit :is necessarythatfi the potential divider .18 .be so: adjustedsthat stea'dy zpositive bias is applied-to :theugrid 1 1 in additiontoithe alternating. bias so: that the lumped voltage over; the .valvezis not-izer-o'. By this neansiit? has: been foundthattthe sensitivity" of v the receiveris "substantially indee pendent ofivariations in the'strength:oftosciil lations generated in the circuit3landi32 of:,t-hesecondevalve duesfcrxex ampleito.vaiZiationsinithe vo-ltage .tifithe battery T i It will be appreciated that, while fourtemk bodiments .Ql'f. the ginventionjhave been describedv "by way I of example the. invention is by no means limited to these four embodimerits, and many modifications may be made without departing from the scope of the invention.

We claim as our invention I 1. In radio receiving apparatus wherein oscillations may be generated, a thermionicdevice having a grid and plate,'meansfor providing only alternating potentials on said plate, whereby oscillations in said apparatus will be quenched during negative-potential cycles independently of grid potentials in 7 said thermionic device, and means for biasing 1 said grid to a value insuificientto maintain oscillations during periods of non-reception.

2. In a radio receiving apparatus wherein oscillations may be generated, a thermionic device having agrid and av plate, means for i potential, and means for providing alternating potential on said grid bearing such relationship to the plate potential, whereby plate current characteristics will be main- 1 5 tained substantially uniform.

3. In radio receiving apparatus wherein oscillations may be generated, a thermionic device. having a grid and a plate, means for providingionly alternating potentials on said plate, means for biasing said gridito render said device incapable of oscillating'during periods of non-reception of signal energy, means for providing an alternating potential on said grid in reverse-phase relationship to J25 said plate potential and of a value equal to said plate potential divided by'the voltage amplification factor of the device, .whereb-y plate current characteristics will "be, maintained substantially uniform.

4; In radio receiving apparatus wherein oscillations may be generated, a thermionic device having a grid and a;plate,-means for providing intermittent positive potentials on saidplate, means for providing biasing potential on said grid, said biasing potential having an alternating and a direct component, the negative cycles of the alternating component occurring simultaneously with the positive potentials on the plate,-said negative cycles having a value substantially equal to the plate potential divided by the voltage amplification of said thermionic device, said direct component ofthe grid biasing potential being sufficient to render said device incapable of oscillating only during non-reception periods.

In'testimony whereof We have hereunto subscribed our-names this tenth day of March, 1926'. a i

' WALTER JOHN BROWN.

CECIL REGINALD BURCH. 

